Guest Blogger and Neuroscientist Paul King of the Redwood Center for Theoretical Neuroscience at UC Berkeley weighs in on Quora.
Multiple mechanisms have been identified, however this is an still an area of active research.
In the cerebral cortex, it has been proposed that gamma frequency synchronization (40 – 80 Hz) comes about partially due to the push-pull between excitatory (E) and inhibitory (I) cells. The E cells excite the I cells, which inhibit the E cells. When inhibition wears off, the E cells that spike are more likely to do so at around the same time.
Another proposed mechanism involves gap junctions between I cells. When open, these junctions would cause all connected I cells to fire at around the same time, indirectly causing the E cells to become more synchronized.
In some brain regions, there is a population of (indirectly) connected neurons with a similar natural intrinsic preferred oscillation frequency due to internal calcium ion fluctuation dynamics. The interaction between these neurons, either by direct contact, or mediated by intermediate inhibitory interneurons, leads their spikes to become aligned over time.
It is possible that all of these mechanisms, perhaps with others, operate in parallel and contribute to different synchronicity patterns at different temporal scales.